U.S. patent number 4,298,728 [Application Number 06/155,919] was granted by the patent office on 1981-11-03 for method of preparing hydroxyethyl ethers of cellulose.
This patent grant is currently assigned to Hercules Incorporated. Invention is credited to Thomas G. Majewicz, Walter S. Ropp.
United States Patent |
4,298,728 |
Majewicz , et al. |
November 3, 1981 |
Method of preparing hydroxyethyl ethers of cellulose
Abstract
In preparation of hydroxyethyl ethers of cellulose, ethylene
oxide efficiency of the reaction and solubility characteristics of
the product are improved by using alkali cellulose which has been
prepared in the presence of boric acid or a boric acid salt.
Inventors: |
Majewicz; Thomas G. (Chadds
Ford, PA), Ropp; Walter S. (Hockessin, DE) |
Assignee: |
Hercules Incorporated
(Wilmington, DE)
|
Family
ID: |
22557311 |
Appl.
No.: |
06/155,919 |
Filed: |
June 3, 1980 |
Current U.S.
Class: |
536/96; 536/101;
536/91; 536/95 |
Current CPC
Class: |
C08B
11/08 (20130101); C08B 1/08 (20130101) |
Current International
Class: |
C08B
11/08 (20060101); C08B 1/08 (20060101); C08B
1/00 (20060101); C08B 11/00 (20060101); C08G
059/00 (); C08G 065/08 () |
Field of
Search: |
;536/91,96,101,95 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2415154 |
|
Oct 1975 |
|
DE |
|
2535311 |
|
Feb 1976 |
|
DE |
|
408730 |
|
Apr 1934 |
|
GB |
|
497671 |
|
Dec 1938 |
|
GB |
|
1465934 |
|
Mar 1977 |
|
GB |
|
Primary Examiner: Clingman; A. Lionel
Attorney, Agent or Firm: Alexander; W. Stanley
Claims
What I claim and desire to protect by Letters Patent is:
1. In the process for preparing hydroxyethyl cellulose wherein a
cellulose furnish is reacted with an alkali metal hydroxide to
prepare alkali cellulose and said alkali cellulose is slurried in a
lower aliphatic alcohol and reacted with ethylene oxide, the
improvement which comprises carrying out the alkali cellulose
preparation in the presence of about 1 to 30%, based on the weight
of cellulose of boric acid or a boric acid salt.
2. The process of claim 1 wherein the boric acid or boric acid salt
is present in amount equal to about 3 to 20%.
3. The process according to claim 2 wherein the lower aliphatic
alcohol is tertiary butyl alcohol.
4. The process according to claim 2 wherein the lower aliphatic
alcohol is isopropyl alcohol.
5. The process according to claim 1 wherein the reaction is carried
out in the presence of borax.
6. The process according to claim 3 wherein the reaction is carried
out in the presence of borax.
7. The process according to claim 4 wherein the reaction is carried
out in the presence of borax.
8. In the process for preparing a mixed cellulose ether wherein a
cellulose furnish is reacted with an alkali metal hydroxide to
prepare alkali cellulose and said alkali cellulose is slurried in a
lower aliphatic alcohol and reacted with ethylene oxide and a
second etherifying reagent, the improvement which comprises
carrying out the alkali cellulose preparation in the present of
about 1 to 30 %, based on the weight of cellulose, of boric acid or
a boric acid salt.
9. The process of claim 8 wherein the second etherifying agent is a
long chain alkyl halide.
10. The process according to claim 9 wherein the reaction is
carried out in the presence of borax.
Description
This invention relates to an improved process for the preparation
of hydroxyethyl ethers of cellulose. More particularly, it relates
to a process whereby the yield of the cellulose ether based upon
the concentration of reagents employed is improved and at the same
time the quality of the product is improved as compared to
conventional processes.
Hydroxyethyl cellulose is a well-known and widely used
water-soluble cellulose ether. Its relatively good water solubility
and its good viscosifying powers make it extremely useful as a
viscosifier in a great number of applications. For example, there
is a large market for this material as a thickener for latex paints
and there is likewise a large market for it as a thickener in joint
cements and various types of mortar. Another relatively large
market is as a suspension aid in emulsion polymerizations. In the
immediate future it is forecast that another market, perhaps larger
than those already covered, will be found in various aspects of
petroleum recovery such as, for example, fracturing fluids and in
drilling fluids, as well as for use as a flooding fluid in
secondary and tertiary recovery operations.
Over the years, a number of processes have been proposed for the
preparation of water-soluble hydroxyethyl cellulose. Basically all
of these processes involve treating cellulose with alkali and
reacting the resultant alkali cellulose with ethylene oxide. This
can be effected in a dry process in which no additional diluent is
added and the gaseous ethylene oxide reacts directly with the
doughy or pasty alkali cellulose product. Preferably, however, the
reaction is carried out via a slurry process wherein the alkali
cellulose is slurried in an inert organic diluent for reacting with
ethylene oxide. The preferred such diluent is a lower aliphatic
alcohol, most preferably, a 3- or 4-carbon alcohol such as
isopropyl or tertiary butyl alcohol.
Tertiary butyl alcohol (TBA) and isopropyl alcohol (IPA) are by far
the preferred inert diluents for use in the preparation of
hydroxyethyl cellulose. Between the two, however, it is not
possible to select a preferred diluent. Each has its own strong and
weak characteristics which are balanced by the strong and weak
characteristics of the other.
TBA as a diluent is superior to IPA in terms of ethylene oxide
efficiency. Ethylene oxide efficiency is defined as the ratio of
moles of ethylene oxide add-on per anhydroglucose unit (i.e., M.S.
of the product) to moles of ethylene oxide input per anhydroglucose
unit, expressed as percentage. Thus, with TBA as the diluent, a
preselected ethylene oxide add-on level can be achieved with a
smaller ethylene oxide input than would be required to achieve that
same level with IPA as the diluent. In general, the advantage is on
the order of about 65% efficiency for TBA versus about 50% for
IPA.
When IPA is used as the diluent, on the other hand, good solution
quality of the hydroxyethyl cellulose is realized at a lower
ethylene oxide add-on or M.S. level than is the case with TBA
diluent. With IPA, excellent solution quality is achieved at an
M.S. level of about 1.9 and up as opposed to 2.5 and up required
for good solution quality using material prepared in TBA. Moreover,
with IPA, it is usually noted that the product has a higher
viscosity than does the product prepared in TBA.
Obviously, the development of a process in which one could realize
the good efficiency of the TBA process in combination with the
superior solution properties of the TBA process is much to be
desired. Accordingly, a substantial amount of effort has been
expended in this direction but such effort, to date, has met with
little or no success. Now, according to this invention, a method is
provided by which both objectives can be met using TBA as the
diluent, and which also further increases the quality of the
product prepared using TBA as the diluent.
In accordance with this invention, an improvement is effected in
the process for preparing hydroxyethyl ethers of cellulose wherein
a cellulose furnish is reacted with an alkali metal hydroxide to
prepare alkali cellulose and said alkali cellulose is slurried in a
lower aliphatic alcohol and reacted with ethylene oxide or a
mixture of ethylene oxide and a second etherifying agent, which
improvement comprises carrying out the alkali cellulose preparation
in the presence of boric acid or a salt of boric acid. The boric
acid or boric acid salt is used in an amount equal to about 1 to
30%, preferably 3 to 20%, by weight based on the weight of dry
cellulose.
The boric acid salts which can be used are any of the salts of
orthoboric acid, i.e., those which ionize to form borate ions.
These include any of the alkali metal borates such as sodium and
potassium orthoborate and the various hydrates thereof. The most
common borate and a preferred material to use is sodium tetraborate
decahydrate, also known as borax.
The effects of the process according to the invention are
particularly noticeable when TBA is used as the diluent. A
measurable increase in ethylene oxide efficiency is noted even
above the inherently high efficiency normally experienced with TBA.
More significant, however, is the dramatic improvement in
solubility characteristics of hydroxyethyl cellulose produced by
the process.
Solubility characteristics are evaluated by three parameters:
(a) Solution granularity--defined as undissolved gel particles, is
measured on a subjective scale from 0-5, with 0 signifying the
lowest granularity level;
(b) Solution quality, which is a subjective measure of the clarity
of a solution of the polymer in water; and
(c) The ethylene oxide add-on or M.S. level required to achieve
good ratings in (a) and (b).
The solubility characteristics of hydroxyethyl cellulose produced
by the process of this invention in TBA are dramatically improved
in all three respects over those of hydroxyethyl cellulose produced
in TBA in the absence of borate ions. In fact, solubility
characteristics are improved to the point that they are comparable
to those of hydroxyethyl cellulose produced conventionally in
IPA.
When the process of the invention is carried out in IPA, the same
effects are noted. In IPA, the improvements are less dramatic but
nonetheless real.
The invention has been described to this point in terms of its
utility in the preparation of hydroxyethyl ethers of cellulose. It
is also useful in the preparation of water-soluble hydroxyethyl
ethers of cellulose in which the hydroxyethyl radical is the
principal substituent but in which a second substituent is also
present, usually in a smaller amount. Thus it can be used in the
preparation of, e.g., water-soluble propyl hydroxyethyl cellulose,
ethyl hydroxyethyl cellulose, methyl hydroxyethyl cellulose, and
carboxymethyl hydroxyethyl cellulose.
The invention is highly valuable in the preparation of so-called
hydrophobically modified hydroxyethyl cellulose which contain, in
addition to the hydroxyethyl radical in amounts sufficient to
impart water solubility, a minor amount of a long chain (i.e., 10
to 24 carbon) alkyl group. These products are prepared by reacting
hydroxyethyl cellulose with a C.sub.10 to C.sub.24 alkyl halide,
epoxide, or acid to attach the long chain group. Only minor amounts
of the long chain radical, on the order of about 0.2 to 3% by
weight, are used to yield very sizable increases in solution
viscosity while retaining water solubility. These products and
their preparation are fully described in U.S. patent application
Ser. No. 11,613, filed Feb. 12, 1979, and assigned to the assignee
of this application.
The method of the invention is applicable with any type of
cellulose furnish. Wood pulp and cotton linters are the most
commonly used furnishes. In fact, by the method of the invention,
it appears to be possible to upgrade a furnish to some extent. That
is to say, a furnish which, for some reason, might be of marginal
quality can produce a useful hydroxyethyl cellulose in the presence
of borate ions. Any cellulose furnish will produce a better
hydroxyethyl ether cellulose more efficiently in the presence of
borate ions.
In carrying out the process of the invention, the borate compound
is preferably dissolved in the alkali employed to prepare the
alkali cellulose prior to steeping the cellulose therein. This
avoids the necessity of preparing a separate solution of the borate
compound. It is possible to carry out the process using a separate
solution of the borate, but in addition to the additional handling
that this requires, there is also the possibility of adding too
much water with the borate solution so that the optimum water to
cellulose ratio for alkali cellulose preparation is not
maintained.
Etherification of the cellulose is carried out substantially the
same as in the usual etherification. The only significant
difference is that with the process of this invention substantially
less ethylene oxide and, when used, less of the second etherifying
reagent need be used to accomplish the same substitution level.
The invention is exemplified in the following examples. Solubility
and ethylene oxide efficiency data for each example are recorded in
the table following Example 5
EXAMPLE 1
To 32.4 parts (dry weight) cotton linters in a stirred autoclave
reactor was added 316 parts anhydrous TBA. After sealing the
reactor and degassing with N.sub.2, 63 parts of 17.5% NaOH having
3.0 parts borax (sodium tetraborate decahydrate) dissolved therein
was added. The mass was agitated for 60 minutes. Ethylene oxide was
then added over a period of 5 minutes until a total of 24.0 parts
had been added. The reaction was carried out at 45.degree. C. for 1
hour, then at 60.degree.-65.degree. C. for 2 hours. The slurry was
then cooled, neutralized, washed three times in 80% acetone,
finally in 100% acetone and dried.
Simultaneously a control run was carried out in which no borax was
employed.
EXAMPLES 2 and 3
The procedure of Example 1 was repeated using different lots of
cotton linters as the cellulose furnish.
EXAMPLE 4
The procedure of Example 1 was repeated using IPA as a diluent.
EXAMPLE 5
The procedure of Example 1 was repeated using wood pulp as the
cellulose furnish.
TABLE I
__________________________________________________________________________
Example Cellulose EO Granu- No. Furnish.sup.(f) [Borax].sup.(a)
Diluent MS.sup.(b) Efficiency Viscosity.sup.(c) Turbidity.sup.(d)
larity.sup.(e)
__________________________________________________________________________
1-C B 0% TBA 1.9 66% 6400 SH 4 1 B 9.0 TBA 2.0 71 5900 Cl 1 2-C C 0
TBA 1.9 67 6000 SH 5 2 C 9.0 TBA 2.0 71 5100 Cl 1+ 3-C A 0 TBA 2.3
65 5700 Cl 3 A 0 TBA 2.4 66 5200 Cl 2+ 3 A 3.0 TBA 1.9 70 5750 Cl 2
A 9.0 TBA 1.95 70 6160 Cl 1 4-C A 0 IPA 1.9 47 6100 Cl 2+ A 0 IPA
1.8 46 6500 Cl 2+ A 0 IPA 1.9 48 5700 SH 3 4 A 9.0 IPA 2.0 52 6100
Cl 1 A 15.0 IPA 2.1 53 5950 Cl 1 5-C D 0 TBA 1.9 66 1740 Cl 4 5 D
9.0 TBA 2.0 71 1500 Cl 2
__________________________________________________________________________
.sup.(a) [Borax] = weight per cent based on cellulose. .sup.(b) MS
values based on weight gain, accounting for ash and per cent
moisture. .sup.(c) Brookfield viscosity of 1% aqueous solution at
30 rpm, room temperature, #4 spindle. .sup.(d) SH = slightly hazy;
Cl = clear. .sup.(e) Granularity is measured on a subjective scale
from 0-5, with 0 signifying the lowest granularity level. .sup.(f)
Furnishes A, B and C were cotton linters; furnish D was wood
pulp.
EXAMPLES 6 and 7
Hexadecyl modified hydroxyethyl cellulose containing various levels
of C.sub.16 modifier was prepared using the following recipe:
______________________________________ Ingredient Parts/Part Dry
Cellulose ______________________________________ TBA 8.64 Acetone
0.95 Water 1.56 17.5% NaOH solution 0.30 Ethylene oxide 1.50
Hexadecyl bromide 0.075 or 0.10 Borax 0.10
______________________________________
The cellulose furnish was wood pulp.
The borax was dissolved in the alkali solution and the TBA, acetone
and water were mixed together. A stainless steel reactor, the
alkali/borax solution and the solvent mix were purged with dry
nitrogen. Most of the solvent mix was added to the reactor,
followed by the alkali/borax solution. The wood pulp was then added
as rapidly as possible, using a portion of the retained solvent to
wash down the reactor wall. The mass was agitated under a nitrogen
blanket for one hour at 15.degree.-20.degree. C.
Ethylene oxide was dissolved in the remaining solvent mix and added
to the reactor in one addition. The reactor was sealed, the
temperature was raised to 60.degree. C., and held for 30 minutes,
at which point the pressure had increased to 20 p.s.i.g. The
temperature was then raised to 75.degree. C. During the first hour
at 75.degree. C., the pressure dropped to 9 p.s.i.g. and remained
there.
When the pressure stabilized at 9 p.s.i.g., hexadecyl bromide,
dissolved in the solvent mix, was added and the temperature was
increased to 95.degree. C. for two hours.
At the end of the two hour period, the reactor was cooled to
between 40.degree. and 45.degree. C., pressure was released and 45
parts 70% HNO.sub.3 was added, dropwise, after which the pH of the
mass was adjusted to 6.0 with glacial acetic acid. The product was
separated on a sintered glass filter and washed four times with 80%
acetone. A final wash was done with 100% acetone to reduce moisture
content to about 1%, followed by drying overnight at 70.degree.
C.
In the following table, the increased etherification reagent
efficiency (demonstrated by increased yield of product) and the
increased solution viscosity resulting from the process of the
invention are shown and compared with product prepared without
borax.
______________________________________ Ex. Product wt. % C.sub.16
Viscosity*** No. C.sub.16 H.sub.33 Br** Recovered* Subst. 2% 1%
______________________________________ 6-C* 0.1 160 1.0 80,000
17,000 6 0.1 174 1.0 100,000 23,000 7-C* 0.074 160 0.7 41,000 5,000
7 0.074 174 0.69 95,000 23,000
______________________________________ *Control no borax
**Parts/part cellulose ***Centipoise, Brookfield viscometer, 6
r.p.m.
* * * * *